Field of the Invention
The present invention relates to a process for the detection of a defect of an automotive vehicle battery. More especially, the process according to the invention is intended to be built into an electronic computer carried on board an automotive vehicle, and to warn the driver of an impending defect of the battery.
A certain number of battery defect detection processes already exist. The best known processes consist in measuring the discharge voltage of the battery when the latter is disconnected from the vehicle. This is scarcely practical for regular monitoring of the state of charge of the battery.
Battery defect detection processes also exist which are built into an electronic computer carried on board a vehicle and which require no disconnection of the battery. Such a process is described for example in the document U.S. Pat. No. 4,937,528. However, the implementation of this process requires the monitoring of a considerable number of parameters and hence the addition of specific sensors, thereby correspondingly increasing the cost of production.
The document FR 2 694 660 describes, for its part, a device for detecting a defect of battery elements for a battery intended for powering an uninterruptible power supply device. Such a device is not intended to be implemented in an automotive vehicle. This document teaches however how to measure the changes in the discharge voltage of the battery over time so as to determine any signs of a defect. For this purpose, it is presupposed that the discharge voltage varies almost linearly over time. However, in the case of a battery powering an automotive vehicle, the discharge voltage of the battery during the engine starting phase is greatly disturbed by the operation of the engine. In particular, this discharge voltage is not a linear function of time. This is because the operation of the engine causes considerable oscillations of this discharge voltage during the starting phase. Hence, the straightforward tracking at determined time intervals of the changes in the discharge voltage of the battery is not directly indicative of its state of charge and the teachings of the document FR 2 694 660 are not applicable.
The document DE 3901680 describes a process for monitoring the possibility of cold starting of an internal combustion engine battery. For this purpose, it is proposed that the changes in the battery voltage be measured during the starting phase and that the state of charge of the battery be deduced from the difference between the maximum voltage and the minimum voltage measured.
However, these maximum and minimum voltages are measured at arbitrary instants of the combustion cycle, and their arithmetic difference is therefore dependent on the state of the battery and the normal fluctuations of the combustion cycle. Such a measurement process does not make it possible to circumvent the disturbances related to the combustion cycle of the engine.
The aim of the present invention is to alleviate these drawbacks and in particular to propose a process for detecting automotive vehicle battery defect during the engine cranking phase, said process being capable in particular of circumventing the disturbances related to the combustion cycle of the engine. One seeks moreover to measure the fewest possible parameters and not to use specific sensors. In the case of a slight defect (that is to say one which has not prevented the vehicle from running), it is desired that the driver nevertheless be warned of the state of low charge of the battery so as to carry out a recharge or a change of battery before the latter is completely flat.
For this purpose, the present invention relates to a process for the detection of a defect of an automotive vehicle battery of the type consisting in analyzing the time dependence of the discharge voltage across the terminals of the battery, characterized in that it consists in:
measuring at least two successive values (U1, U2) of the discharge voltage of the battery, during the phase of cranking the engine of the automotive vehicle, for at least two consecutive top dead center points,
taking a difference of the measured voltage values, and
deducing therefrom whether the battery is charged or defective.
Thus, by making measurements of the discharge voltage at well-determined instants of the engine combustion cycle, it is possible to reveal signs of battery defect, without specific sensors, and while circumventing the disturbances related to the combustion cycle of the engine. Measurement of the battery voltage is, indeed, already used in computers for controlling engine operation.
By carrying out the measurements of the discharge voltage of the battery at these specific operating points it is possible to determine very rapidly (during the few engine revolutions of the cranking phase) whether or not the battery is correctly charged. This is because the measurement of the voltage of the battery outside the starting phase is disturbed by the fact that once the engine has started, the battery is recharged by the alternator. It is therefore much more complicated to try to determine the state of charge of the battery and especially its capacity to ensure correct starting of the vehicle outside the engine cranking phase.
It will be noted that the indication of a battery defect is given by a straightforward difference between the values of the voltage at two consecutive specific operating points.
Other objects, advantages and characteristics of the invention will become further apparent from the description which follows, by way of non-limiting example, and with reference to the appended drawings, in which: